How do i run first for loop before going on to the next?

   for Clock1 = repstorage.Levelstime[levelpicker].Value, 0, -1 do
        clock.Text = Clock1
        print(Clock1)
        if Clock1 == 0 then
    lightdoor1:Clone().Parent = game.Workspace.ElevatorModel1.Doors
    lightdoor2:Clone().Parent = game.Workspace.ElevatorModel1.Doors
    game.Workspace.RunningLevel[levelpicker]:Destroy()    
        else wait(1)

        for i = 20, 0, -1 do
        clock.Text = i
        print(i)
        if i == 0 then     game.Workspace.ElevatorModel1.Doors.LDoor:Destroy() game.Workspace.ElevatorModel1.Doors.RDoor:Destroy() break
            else wait(1)

I want first for loop to finish before going to the next